1. Field of Invention
The field of the currently claimed embodiments of this invention relates to systems and methods for detecting and classifying the severity of retinal disease.
2. Discussion of Related Art
Age-related macular degeneration (AMD) is the leading cause of blindness if left untreated throughout much of the western world for individuals over age 501. Vision loss can occur from the advanced stage, which includes choroidal neovascularization (CNV) or geographic atrophy involving the center of macula. The advanced stage can lead to severely impaired central vision, impacting everyday activities2. In the United States, approximately 200,000 individuals over the age of 50 develop the advanced stage of AMD each year in at least one eye3. Left untreated, approximately 70% of these cases develop substantial vision loss in the affected eye within 2 years. Furthermore, of those patients who developed advanced AMD in only one eye, approximately half will develop the advanced stage in the other eye within 5 years, resulting in a high risk of developing legal blindness if left untreated1.
Although there is no definitive cure for AMD, the Age-Related Eye Disease Study (AREDS) has suggested benefits of certain dietary supplements for slowing the progression of the disease from the intermediate stage to the advanced stage4. In addition, recent clinical trials of anti-vascular endothelial growth factor (VEGF) for treating CNV can eliminate a substantial proportion of cases which otherwise would progress to the advanced stage5. The better the visual acuity at the onset of anti-VEGF therapy, the greater is the chance of avoiding substantial visual acuity impairment or blindness2. Thus, it is critical to identify in a timely manner those individuals most at risk for developing advanced AMD, specifically, individuals with the intermediate stage of AMD.
The following drusen classification method was adopted by the AREDS Coordinating Centers6: large drusen are defined as those that exceed 125 microns in diameter (the average size of a retinal vein at the optic disk margin), small drusen are defined as those with diameters less than 63 microns, and medium-sized drusen are defined as those with diameters in the range between 63 and 125 microns. The intermediate stage of AMD is characterized by the presence of numerous medium-sized drusen, or at least one large druse within 3000 microns of the center of the macula (FIG. 1). While a dilated ophthalmoscopic examination at least every 2 years to detect asymptomatic conditions potentially requiring intervention, such as the intermediate stage of AMD, is recommended by the American Academy of Ophthalmology [AAO PPP], the presence of drusen often causes no symptoms and therefore no motivation for an individual to seek examination by an eye care provider to detect an asymptomatic intermediate stage.
Currently, ophthalmoscopy of the retina by trained health care providers (including ophthalmologists) or evaluation of fundus photographs by trained graders (including ophthalmologists) remains the most effective method to identify the intermediate stage of AMD1. However, grading fundus images manually by a grader can be a tedious process requiring the expertise of an adequately trained health care provider or extensively trained fundus photograph grader to understand the varying patterns recognized by an ophthalmologist7. Furthermore, access to an ophthalmology health care provider at least every 2 years to detect the intermediate stage of AMD after age 50 can be challenging for many health care environments. Therefore, there is a need for automated visual diagnostic tools to facilitate the detection of the intermediate stage AMD among a large pool of the at-risk population. As an example of the potential health care burden of this issue, in 2010, in the United States, there were about 98 million individuals over the age of 50 and this number is projected to increase to approximately 109 million by 20158.